264 



PEOE. OWEN ON THE OEDEE THEEIODONTIA, 



(fig. 2, c) at the fore part of the depression for the reception of 

 the upper one. 



The breadth of the base of the exserted crown of the npper canine 

 is 5 millim. ; it rather suddenly narrows to the pointed end ; the 

 length of the preserved exserted crown is 12 millim., a small part 

 of the apex being wanting. The crown is slightly compressed, with 

 a trenchant border on the hinder part which inclines somewhat 

 inward ; there is an indication of a fine crenation of this border. 



On the left side (PI. IX. fig. 2) I had the outer alveolar wall of 

 the canine removed and exposed its root (c), extending upward and 

 slightly backward for twice the length of the exserted crown. The 

 root, as it rose, slightly expanded beyond the breadth of the crown, 

 and as gradually and slightly narrowed to the open end of the pulp- 

 cavity. There is not a trace of a successional canine ; and the con- 

 dition of the pulp-cavity and petrified pulp, discoloured by the iron 

 of its blood, indicates renewal of the working part of the laniary by 

 continuous growth. In the course of this expository operation the 

 exserted crown of the mandibular canine (ib. c') was exposed, 12 

 millim. in length, nearly that of the corresponding part of the maxil- 

 lary canine, in front of which it extends, but along the inner or median 

 level, so as to have been wholly concealed (as shown on the right 

 side, fig. 1) by the alveolar plate continued from the upper canine 

 to the upper and outer incisor. There are few instances of carni- 

 vorous air-breathers in which the mandibular teeth are so completely 

 covered and hidden by the upper jaw, when the mouth is closed, as 

 in this and other Theriodont Eeptiles. 



After an interval about equal to that between the upper canine 

 and outer incisor, the molar series (ib. figs. 1 & 2, m) commences, 

 behind the canine. Of this series the crowns of five are exposed on 

 each side of the upper jaw ; they are all of the simple, slender, 

 laniary type ; the four anterior ones are divided by intervals of 

 about the basal breadth of those teeth, which is 1J millim. in the 

 first and second molars, and diminishes to 1 millim. in the fifth • 

 the crown, inclining a little backward in the three hindmost, gra- 

 dually narrows in each molar to a sharp point ; the alveolar extent 

 of the five molars is 7 millim. 



The toothless extent of the maxillary to beneath the fore border 

 of the orbit is 13 millim. The upper dentigerous tract in a straight 

 line from the foremost incisor to the hindmost molar is 45 millim. 



On a cursory comparison of the Theriodont genera and species 

 now made known we discern a considerable range of variety in both 

 size and shape. 



The extremes of size are exemplified by Titctnosuclius ferooo * and 

 Scaloposaurus constrictus f ; those of shape by the flattened head of 

 Galesaurus % and the compressed head of JElarosaurus (PI. IX.). 

 The skull of Procoloplion § is broad in proportion to its length ; that 



* Quart. Journ. Geol. Soc. vol. xxxv. (1879), p. 189, pi. xi. 

 t Catalogue, ut supra, p. 24, pi. xvi. figs. 10-15. 

 X Quart. Journ. Geol. Soc. vol. xvi. p. 58, pi. ii. 

 § Catalogue, ut supra, p. 25, pi. xx. figs. 4-7. 



